acrylic tank bowing and strange scratches?

[xeanliao]

Hi, I noticed the attached acrylic 75g fish tank has a little bowing on front and back with or without water in it, probably less than half inch. The tank is 48 inch long 18 width, 20 inch height. It also looks like 3/8 thickness to me.

Also, it has a lot tiny half-inch long hair lines all in the same directions, they are hard to see but reflecting lights from certain angle with lights in the background.

I am doing the simple leak test now, just worry a bit about long term safety stuffs. Do you think these are signs of the material getting too old, or any safety concerns, etc, that is better not to set it up? Hoping you can see any concerns from the attached pic, and thanks in advance.

 

[sunken3]

i assume it is a used tank? and when you say bowing, you mean when filled with water...?

 

[xeanliao]

i assume it is a used tank? and when you say bowing, you mean when filled with water...?

Yes, it a a used tank that I don't know how old it is. It is bowing without water as well (good question, let me modify my original post).

 

[sunken3]

i can't see the scratches or the bowing. however, I have several acrylic tanks and over time they seem to get spider cracks and stress looking fractures (all superficial).. i think it is age and maybe UV lighting over time. Additionally acrylic tanks bow alot (my 40 gallons (36" long) - bows at least a 1/2 or more).. the bow you have may just be "memory" from having the bow in it for so long. i have never (knock on wood) had an acrylic tank leak -i have some in the 20 year range (though they do yellow and start to be best as sumps or QT tanks.. )

 

[xeanliao]

i can't see the scratches or the bowing. however, I have several acrylic tanks and over time they seem to get spider cracks and stress looking fractures (all superficial).. i think it is age and maybe UV lighting over time. Additionally acrylic tanks bow alot (my 40 gallons (36" long) - bows at least a 1/2 or more).. the bow you have may just be "memory" from having the bow in it for so long. i have never (knock on wood) had an acrylic tank leak -i have some in the 20 year range (though they do yellow and start to be best as sumps or QT tanks.. )

Thank you, you described much better than the picture itself: "spider cracks and stress looking fractures."

 

[((FORDTECH))]

Thank you, you described much better than the picture itself: "spider cracks and stress looking fractures."

I have a 300 gallon acrylic in basement and omg does it bow when full of water. I got it used and first time filling I didn’t even want to stand in front of it. Been running 6 months now no issue but I still think about it.

 

[xeanliao]

I have a 300 gallon acrylic in basement and omg does it bow when full of water. I got it used and first time filling I didn’t even want to stand in front of it. Been running 6 months now no issue but I still think about it.

lol ... I think this will haunt me for a long time as well, I actually have a glass tank now, but being paranoid all the time what if earthquakes strike someday given I live in CA. So I decided to get a cheap acrylic tank to replace my glass tank thinking it must be safer/stronger enough. Being a paranoid person, I am not sure what I going to do now :-(

 

[sunken3]

lol ... I think this will haunt me for a long time as well, I actually have a glass tank now, but being paranoid all the time what if earthquakes strike someday given I live in CA. So I decided to get a cheap acrylic tank to replace my glass tank thinking it must be safer/stronger enough. Being a paranoid person, I am not sure what I going to do now :-(

i live in CA and have always had acrylic (except for some glass nano's and such). i decided to upgrade my 120 and 60 (acrylic) to a 250 glass.. beside the fact that i can lift a 120 acrylic by myself and the 250 was the near death of me and 3 other big guys.. i always have the earthquake fear in my mind. we have had a few to date (quakes), and so far no issues... of course big enough and it wont matter if its glass or acrylic - it'll come down.

i liked the glass because honestly.. it seems clearer than acrylic.. no matter what the claims are.. it also doesn't scratch nearly as easily (though i did manage to put a nice one right down the center moving a frag rack... UGH!). i feel 1000% safer with acrylic though.. i always feel in a glass tank if a rock falls, or something hits it, it's going to shatter..

 

[xeanliao]

Thank you, you described much better than the picture itself: "spider cracks and stress looking fractures."

@sunken3 : after more googling, I think it is also called "crazing". do you concern about the durability given the amount of the crazing shown in the picture above?

 

[ca1ore]

Yes, it's stress crazing. Happens when the panels bow for longer periods of time. I do not know, however, how problematic it is. I had my acrylic tank made thicker than 'recommended' so that there would be no bowing and so far I have had no crazing.

 

[fade2black]

3/8" is too thin for a 75, even with a supported top. For a tank that is 20" tall, 1/2" is the minimum thickness I would use. Probably why you see so much bowing and the crazing.

 

[sunken3]

3/8" is too thin for a 75, even with a supported top. For a tank that is 20" tall, 1/2" is the minimum thickness I would use. Probably why you see so much bowing and the crazing.

maybe.. i have a 120g (its a 1/2" thick).. 60g cube is 3/8".

my 250g is 1/2" glass - which is the norm.

 

[sunken3]

@sunken3 : after more googling, I think it is also called "crazing". do you concern about the durability given the amount of the crazing shown in the picture above?

if its from a reputable tank maker i wouldn't worry. homemade.. a whole different story (but that's just me).

 

[vetteguy53081]

Crazing will happen no matter how thick the acrylic is. A little bowing is NOT abnormal. Should be of no concern, However, if you need to be placed at ease, Consider Euro-bracing the tank which will cost very little in Materials

 

[sunken3]

Crazing will happen no matter how thick the acrylic is. A little bowing is NOT abnormal. Should be of no concern, However, if you need to be placed at ease, Consider Euro-bracing the tank which will cost very little in Materials

aren't all acrylic tanks top braced?

 

[vetteguy53081]

aren't all acrylic tanks top braced?

Nope. My drop off tank is acrylic and Not braced. Most AIO are not either. Below are examples of eurobracing.

 

[CMMorgan]

I +1 @vetteguy53081, Eurobracing would make a big difference. The 3/8" thickness is a bit thin for a tank that size. I've got one on order that is 3/4" thick... still eurobraced.

 

[sunken3]

Nope. My drop off tank is acrylic and Not braced. Most AIO are not either. Below are examples of eurobracing.

i live such a sheltered life.. all my acrylic tanks are clear for life.. all fully braced on top.. learned something new.

 

[KrisReef]

I would buy a new tank if it bothered me.

I have an old skimmer that has stress cracks that look similar to those shown in the first photo. Acrylic and stress cracks and bowing over time come with that material.

I do not know if I would add Euro-bracing to an already warped tank. When I've tried to glue acrylic with stress cracks the area around the solvent application always develops many more new stress cracks (-crazing) around any solvent joint. Also, I think that trying to fit a flat piece of acrylic to a warped panel would require a lot of work to fit properly. A

Fill it outside, if it holds water it will probably be ok for at least a few more years. If you can't sleep thinking that the tank will explode then upgrade to secure your sleep.

 

[fade2black]

maybe.. i have a 120g (its a 1/2" thick).. 60g cube is 3/8".

my 250g is 1/2" glass - which is the norm.

You can't compare glass thickness to acrylic. It's apples and oranges. And just because someone did, doesn't mean they should have or even know what they are doing. The acrylic thickness is meant to minimize bowing and shear stress on the joints as well as giving sufficient contact area to create a strong joint. A lot of variables here to take into consideration. The important part to consider when determining acrylic thickness is the height and the length. Height is of utmost importance. Going by Cyro, the acrylic manufacturer, they recommend just over 1/2" for a tank 20" high with a eurobraced top.